qwck10th

How much metal do I have to leave under the bridge? Looks like the port is between 6-7mm thick there. Can I take it down to 4mm, or 3, or less? I don't know how much mechanical/thermal stress the bridge is under...

Bridge parts and rotors don't mix

Thanks,
Steve Cappelli.
Marietta, GA

- right behind ya Grizzly


Pic to clarify, hopefully...

WackyRotary

I don't know, exactly, except to say mine didn't break. The key is not how thin but how good the transitions are from port runner to the port hole. It should be somewhat smooth since airflow is less then optimal and resists sharp corners somewhat.

Grizzly

I take it you mean the Bridge its self? Mine is 5mm wide and i left quite alot on 5-6mm but i sort of knife edged it so if flowed better.

i would ask the Experts though because this is my first Bridge and i have not done many miles on it. (Hopeing it will take the power?)


Good luck.

WackyRotary

Well the first thing you learn in Superflow flowbenching is it that items with razor sharp edges tend to slow the flow if they are in a critical spot. When you just flow a port on head without the whole intake on for example, you need to have somekind of attachment on were the intake is to smooth out the edge otherwise it will not reveal any changes because the sharp edge is screwing it all up. This is more critical in some areas of a port then others...which I learned the hard way when we had a competion in a class I took when we were altering the port runners in a Ford Essex hemi head. In the center of the port, flow is relatively smooth but slower. But near certain edges, the flow is faster and what the air is sliding against will be more turbulant which may help lower engine speeds, since it will keep the mixture better mixed, but will likely be a restrictor when you ask your engine to draw more air through the ports at upper rpm. It all depends on how you want your engine to drive like I suppose.

Grizzly

I did'nt know that !

When i did mine i left a 5mm bridge then i did'nt realy make it thiner but i tapered it of, I would'nt say it is sharp but it does taper off to about 1.5-2mm rad.

I'm not very experianced in the Gas Flowing world (this is my first bridge) and i do appreciate your input (i can never get enough information on Tunning these Rotory engines).

I hope i have'nt messed this up it took me along time to get the Port Exactly how i wanted it?

SPZ510

Go to Pineappleracing.com and check out there biggest j-bridgeport. That's about how thin you can get a bridge and I believe it's much narrower that 5mm. I did mine at 3.5mm.

qwck10th

I emailed Mazdatrix, and got a reply in LT 24hr
Hope Dave doesn't mind me quoting...
I agree that 3.5 looks about right. I'd do less if I thought it'd hold.

L8r,
Steve C.
I see my avatar is making the rounds
Car and dyno sheet in the .sig.

maxcooper

Everytime I see the subject of this thread, I think of the BeeGee's song "How Deep is Your Love". There must be something seriously wrong with me.

-Max

SPZ510

I was told that it is not the thickness of the bridge that really matters like we've been talking about, but how "deep it is. I was told the when the bridge breaks it breaks toward the rotor or up/down if you lay the housing on its side. The bridge is just there to support the corner seal. At least that was what I was told. I stopped at 3.5mm and my bridge is about the same deep. It looks pretty thin to me but I was told I could have gone even further and it's been done before. I'll post some pics tonight. I was pretty scetched when I was doing it.

qwck10th

Love to see those pics!

Bad news for me tonight (but maybe a silver lining...). Seems I got a little carried away blending the bridge into the main port... Now I see a sliver of daylight (actually 500w halogen worklights) at the top of the runner (hello water jacket!). Actually, I'm glad I broke through - I'd rather find out there was only .0005" of metal there now than at 15psi and WOT!

If I find the right stick, I think I can clean up the area and weld a bead on the water jacket side. We'll see. Next housing, the micrometers come out!
Sigh...

SPZ510

Ok, here's a pic of my port. I'm not sure how to post the link but I'll try. If it does'nt come out just go to the forum photo galery under misc.
Please be kind this is my first bridge port ever and before this I new nothing about rotaries. I still don't know much just listening carefully. I still have to touch up a couple places and if you look carefully you'll see what I mean.

https://www.rx7club.com/photo/index.php?photo=1007

BOOSTD 7

JB Weld is your friend ....

qwck10th

R, are you saying you'd prefer JB over a weld (assuming a good weld can be made)? Do you know someone that has attempted this?

I'll try to get some pics up tonight.

s

qwck10th

Full sized gallery is here. The red thing is a spray nozzle from a can of WD40. Many thanks to Arthur from theDynolab for the use if his digi-cam.

Here's the thumbnails.
..

..

..

Judge Ito

Judge Ito

I personally don't like to weld. Remember when u have ported into the runner to the point where u go into the water jacket that complete area is very thin from trying to create a nice flow, as soon as u put some heat and try to weld into the cast iron, your going to make a bigger hole, this is from the casting being very thin. I have used JB weld for many years and got great results from it. Rob from Pineapple Racing told me that there's a product out there that will put JB weld to shame, it's called Mastic Plastic. If u want more info. on Mastic Plastic let me know. And as far as your "first" bridge port U did a great job. When I Port a bridge or serious street port, I always port into my water jacket. I have a customer engine 5 years and running with some JB Weld holding on to the side housing for dear life

qwck10th

Thanks Judge!
Judge Ito wrote: Yeah, I looked at the Mazdatrix images, and they have a cut-away of the housing. its a lot thinner than I thought... I should have measured. No welding... I found this stuff at a place called Micro-Market. Is this it?
Thanks! I have a lot of experience with composites and epoxies, but not JB Weld, or Mastic Plastic. I'm glad to hear JB holds. I've got some downstairs. Looks like its time to open it up.

I was pretty discouraged before I read your post. I'm feeling much better now... Ready to put those carbide cutters to work.

Thanks again for the encouraging words.

Steve C.

WackyRotary

Man, I don't know why mazda made the water jacket so thin in that area, afterall the intake is not hot like exhuast ports I think

Judge Ito

Hey Steve I look at every rotary enthusiast like a member of my rotary family. Steve forgot to tell u Racing Beat recomends Devcon too. I have used it with good results too. here is a link to devhttp://www.devcon.com/devconsecondaryframeoem.htmlcon epoxy...

AJC13B

Devcon is used by just about all Australian rotor shops for use on BP and PPs....

RICE RACING

Half my motor is DEVCON !

Node

iTrader: (1)

wow, thats really cool how the 2 part epoxy on the mastics stuff is. Just a tube. Reminds me of the gum from Mission Impossible.

Felix Wankel

Are you gonna relieve the rotor housings too? I always wondered what you do with the O rings.

(I want a bridgeport for my new engine, I'm just trying to make sure I don't screw up too bad building it )

qwck10th

I am going to relieve the rotor housings. After c'speed's comments, and fitting a housing over the end plate, there's no doubt its gonna get cut. Since I'll be doing it by hand, I'm thinking about making a jig for the job - keeping the depth right looks tough. The pic's on Mazdatrix's site are what I'll be going by - very helpful.

I had half-a-thought about cutting through the o-ring (doing a "big" bridge), but I've already got my hands full with a standard bridge - maybe next time.

Thanks for all the help.
You guys rock!
Steve C.

peejay

I used lots of JB Weld in the intake manifold I modified a year ago, and when pulling the engine apart this weekend I noticed that the JB Weld was shrunk down so that it was no longer flush with the aluminum (I swabbed the goo in to fill ports/low spots before porting) and in some places was actually eroded away. When I did the work, I only let the stuff dry for a little over 24 hours for each application, before porting - was this not long enough (shrunk down more after I ported) or does gasoline erode it away?

I know lots of people use the stuff when modifying ports/manifolds/etc so I have total confidence in the product, but the erosion and shrinking kinda worries me.